US Re 27617 discloses a known type of louvred film for controlling the output angle of light from a display. The film comprises alternating transparent and opaque layers in an arrangement which is similar to a Venetian blind. Such an arrangement passes light which is propagating in a direction parallel and nearly parallel to the planes of the layers but absorbs light propagating at larger angles to these planes. Thus, light propagating in undesirable directions is absorbed and this reduces the efficiency of light utilisation. This type of light control film is relatively inefficient as a significant amount of light propagating at oblique angles is absorbed by the film.
JP 2004/245918 discloses a similar type of louvered film but modified to comprise transparent, reflecting and opaque layers. Again, light propagating parallel and nearly parallel to the louvre planes is transmitted. Light propagating at higher angles to the planes and generally upwardly is reflected downwardly into a non-viewing region whereas light propagating at higher angles generally downwardly is absorbed. Again, the efficiency of light utilisation is relatively low.
U.S. Pat. No. 5,204,160 discloses a similar type of louvered film to US Re 27617 but modified to include microlenses between the opaque layers. In addition the light absorbing regions are formed from grooves which are filled with absorbing material.
US2006/0245060A1 describes a view angle control sheet consisting of trapezoidal lenses with wedge shaped regions between that are filled with a material of lower refractive index. Further, the document provides formulae for the slope of the wedge shaped regions in terms of the refractive index of the two media. The document claims to reduce the brightness decrease observed with films like that disclosed in US Re 27617. The document also discloses that the wedge shaped regions may be absorbing or contain particles to scatter light.
US2007/0076406A1 discloses a similar type of light control film to US2006/0245060A1, but the application is to widen the viewing angle of a display rather than restrict the viewing angle to a certain range. Also, the document aims to prevent a reduction in contrast by reducing the amount of ambient light that is incident upon the display. US 2007/0076406 relates to a light controlling sheet that is intended for use with a light source portion in order to provide a collimated backlight. In FIG. 1, for example, which illustrates a typical SLM display, a light controlling sheet 50 is provided between the light source portion 4 and a liquid crystal panel, in order to provide a collimated light source. The light control film of this application is designed to be placed between the backlight and the liquid crystal panel.
U.S. Pat. No. 7,236,286 describes a device similar to U.S. Pat. No. 5,204,160 and US2006/0245060A1 with triangular shaped louvers, but with reflective parts under the base of the wedge shapes to reflect ambient light. The base of the wedges are placed towards the ambient illumination and the application is to trans-reflective displays such that the display is viewable in both transmission and reflection. The film performs no function for controlling the viewing angle of the device.
U.S. Pat. No. 6,876,408 discloses a light collimating plate that is intended for use with a backlight to produce a collimated backlight. The light collimating plate is applied to widen the viewing angle of liquid crystal displays by collimating light so that it passes through the liquid crystal layer at substantially normal incidence, and then diffusing the light at the output side of the liquid crystal display (LCD). By passing the light through the LCD in a substantially normal manner, the off-axis birefringence of the liquid crystal, which would normally alter the propagation of light compared to the normal direction, is not used, and so the angular properties of the LCD are improved. The collimating plate is disposed between the lamp housing and the liquid crystal panel, and a diffusing plate is disposed between the LCD and the viewer. The light collimating element consists of circular microlenses on one side of a substrate and circular apertures on the other with the aperture opposite the apex of the microlens. A light shielding layer is formed on the opposite side of the substrate to the microlens and covers an area other than the aperture. A formula is provided for calculating the diameter of the lenses required in terms of the thickness of the substrate, the refractive index of the substrate, and the diameter of the apertures. The diffusing plate consists of a microlens array having, on its flat exit surface, a light shield layer and an anti-reflective coating that are provided everywhere except over light exit areas that are aligned with the optical axes of the microlenses. The diffusing plate is provided with the purpose of refracting light that has passed through the LCD in a substantially normal direction into a wider set of angles, so as to render the LCD viewable by users from all viewing directions.
US2007058127A1 discloses a multiple-view display that is produced using a parallax barrier substrate, and a method of manufacturing a parallax multiple-view display. A number of options for the parallax substrate are described, but it includes a parallax optic comprising a microlens array placed in registration with apertures, and absorbing regions spaced between the apertures. In order to produce a multiple view display, the microlenses must image a plurality of apertures or display pixels, each aperture or display pixel being imaged to a different viewing direction. The application is concerned with increasing the brightness of a multiple-view display, of increasing the angular separation between the viewing windows, and in reducing the cross-talk between viewing windows.
US2007058258A1 is a continuation in part of US2007058127A1 The application again discloses a multiple view display produced by the action of a parallax optic, but now the parallax optic consists of microlenses spaced apart within the display element.
U.S. Pat. No. 6,697,042 is directed specifically to a “backlight assembly for collimated illumination”, and is designed to be used in a display device in which multiple display panels are tiled together. The use of a collimated backlight allows light to pass normally through multiple display panels placed close together. If the resulting light is imaged using a diffusing plate then the gap between the display panels can be made to appear invisible. In this application the “cavity exit plate” shown in, for example, FIG. 3 is clearly intended to be disposed over the exit face of a cavity that includes a number of light sources; there is no disclosure or suggestion of providing the cavity exit plate over the exit face of a display as this would not allow the invention to fulfill the intended application as described above.
U.S. Pat. No. 6,762,883 discloses a lenticular lens sheet having an entrance surface comprising an entrance lens part and an exit surface comprising an exit lens part. Light rays refracted by the lens elements of the entrance lens part is directed to an exit lens part of the exit surface.
U.S. Pat. No. 5,396,350 describes a backlight waveguide. A light source is used to illuminate a waveguide, and light is guided down the waveguide by total internal reflection. Inverted prism features are provided on the surface of the waveguide to extract light from the waveguide.
WO2005/071474 describes a display in which the angular range of output light is controlled, for example into viewing ranges corresponding to intended observer positions.
JP 2007-333867 describes an angle of visibility controlling element including an azimuth difference barrier which has a “shade part S” and a “transparent part T”. The azimuth difference barrier can be created by patterning a light blocking material such as chromium.
U.S. Pat. No. 5,528,319 discloses a privacy filter having two spaced grids, each of which is formed of an array of “blocking members” having transparent space there between.
EP0599451 and US2002/0158967 describe further examples of a privacy filter using a louvre film.
GB2426352 relates to the use of a control element to generate a “confusing image” which is visible at high viewing angles, so that the image on an underlying display can be understood by an observer only at low viewing angles.
US2007/0058127 discloses a display having an image display element and a lenticular array forming a parallax optic. A black mask may be provided between the lenses of the lenticular array.
FIG. 1 of the accompanying drawings illustrates a typical SLM display, 2, of known type. This type of SLM display is common in, for example, such devices as mobile phones, notebooks and automotive displays. It consists of a display, 6, (such as a liquid crystal (LC) display) with front, 24, and rear, 20, polarisers and front, 26, and rear, 22, compensation films for increasing the range of viewing angles. The active part of the LC display typically consists of a front substrate, 36, on which are formed apertures, 40, which may be colour filters and black matrix absorber, 38, and a rear substrate, 48, on which are formed thin film transistors (TFT), 44. Both substrates may also include electrodes (not shown) and alignment layers or other structures (not shown) for aligning the liquid crystal, 42. It can also consist of a backlight unit, 4. This consists of illumination devices (e.g. light emitting diodes, LEDs), 14, a light-guide, 12, a back reflector, 10, a series of backlight enhancement films (BEFs) and diffusers, 16. A BEF film from 3M, 18, may be placed between the backlight and the display panel to enhance the brightness of the display. The viewing angle of the display may be restricted in a particular direction by the inclusion of a Light Control Film, 50, such as the film made by 3M which is of a louvre type. Such films are used as a privacy filter to prevent other people viewing the display, or to prevent unwanted reflections from a car windscreen in an automotive environment or from a cockpit canopy in an aircraft etc.